The Java Boutique: Java Tutorial: Poor Man's Graphics

Tutorials : Poor Man's Graphics :

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One extra feature that you would almost certainly need to have is the ability to "scale" the bars. Say that the numbers for NBC, CBS, and CNN were 3000, 2000, and 3200, then you could not directly use these numbers as the number of pixels for the bar lengths. What you would have to define is how much one pixel should represent. For the latter numbers you could define the scale like this: 1 pixel equals 10 of your units. Thereby the value 3000 would become 300 pixels. A new bean-method could handle this:

public void setScale(float scale)

In the example above we would use it like this:

<%=graph.setScale(10)%>

Note that the scale is of type "float", which allows us to specify a scale like "0.1F", meaning that one of our units equals 10 pixels.

Adding Other Features

It's very easy to add some simple effects to the bars by utilizing well-known HTML-features:

a "tool-tip" can be added to a bar by using the title-option on the img-tag. This could be used to give further information on the poll results.
mouseover/mouseout effects can be added to the bars. This allows you to call JavaScript functions which could be used for other visual effects.

To support older Explorer and Netscape versions you would have to make a hyperlink around the bar-image and then apply the title-option and mouse-events to this hyperlink.

Improving the Bar Charts Further

In the next article I'll show how to make the charts more professional, e.g. by adding an axis, and also how to facilitate using them by making some high-level methods that completely hide the table structures.

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